The present invention relates generally to a device that provides focusing of divergent high-energy x-rays while maintaining good energy resolution, increasing the useful flux by 1000 over standard techniques. The device solves the problem of ineffective focusing of high-energy x-ray beam lines.
An x-ray produced at a light source will spread out or diverge as it travels from the light source. X-rays produced by a beamline with a 5 milliradian divergence, for example, will spread to 5 millimeters (mm) by the time they are 1 meter away from their source, and to 50 mm when 10 meters away. This is a problem for light source scientists, who want the highest possible x-ray flux on a small spot, which requires a well-focused beam.
Previous technologies for x-ray focusing relied on mirror-like surface reflections to focus x rays. These technologies demonstrated that x-rays can be focused by bending a Bragg crystal. This approach was the first which enabled the use of a synchrotron x-ray beam having a large horizontal divergence. In the years since, the technology has improved to minimize the anticlastic bending which degrades performance of this class of focusing monochromator, but such technologies still required large active surfaces as the x-ray energy increases and/or the grazing incident angle decreases. This requirement causes technical difficulties in error control and there are theoretical limitations on the divergence of the x-rays that can be focused. Moreover, serious theoretical and practical limitations remain, limiting such technologies to low x-ray energies and small x-ray divergence.
For X-rays with energies above 30 keV, the Bragg angle is small and it is difficult to implement traditional sagittal focusing. Because of the decreased Bragg angle, the beam's footprint on the crystal increases. Large crystals, of length approximately 100 mm, must be used, making the control of anticlastic bending difficult, if not impossible. For example, sagittal focusing of X-rays from 40 to 60 keV has been recently achieved by combining specialized bender, high-precision cutting of hinged crystals and higher index diffraction to increase the Bragg angle. Also, at high x-ray energies, the energy bandwidth of the monochromatic beam created is dominated by the vertical opening angle of the beam, which is of the order of a few tenths of a milliradian. The resulting energy resolution may be unacceptable for some applications. Finally, the bending radius required becomes extremely small at high x-ray energies, requiring extremely thin crystals, which is impractical for such long crystals.
The recent availability of powerful, third-generation high-energy synchrotron radiation sources, such as the APS in the United States, the ESRF in France, and Spring-8 in Japan, has pushed the spectrum of x-rays to much higher energies than imaginable two decades ago. Since no practical method has been available to focus a large divergence of high-energy x-rays, beamlines at these facilities were forced to use either lower energy x-rays or a tiny part of the large horizontal fan beam.
Accordingly, it would be desirable to provide an x-ray focusing device that focuses a large horizontal divergence (e.g., up to 20 milliradians) of high-energy x-rays (e.g., above 50 keV) without relying on a crystal surface to reflect an x-ray beam. It would be further desirable to provide a device that makes an incident fan of white x-rays (e.g., up to 200 mm wide), from a synchrotron-radiation source, monochromatic with high energy-resolution and focuses the beam to a small point (e.g., less than 0.5 mm wide).